1. Field of the Invention
The field of art to which this invention pertains is the solid bed adsorptive separation of esters of fatty acids. More specifically the invention relates to a process for separating an ester of an unsaturated fatty acid from an ester of a saturated fatty acid which process employs an adsorbent comprising particular zeolites which selectively adsorbs an ester of an unsaturated fatty acid from a feed mixture containing an ester of an unsaturated fatty acid and an ester of a saturated fatty acid.
2. Description of the Prior Art
It is well known in the separation art that certain crystalline aluminosilicates can be used to separate hydrocarbon types from mixtures thereof. As a few examples, a separation process disclosed in U.S. Pat. Nos. 2,985,589 and 3,201,491 uses a type A zeolite to separate normal paraffins from branched-chain paraffins and processes described in U.S. Pat. Nos. 3,265,750 and 3,510,423 use type X or type Y zeolites to separate olefinic hydrocarbons from paraffinic hydrocarbons. In addition to their use in processes for separating hydrocarbon types, X and Y zeolites have been employed in processes to separate individual hydrocarbon isomers. As a few examples, adsorbents comprising X and Y zeolites are used in the process described in U.S. Pat. No. 3,114,782 to separate alkyl-trisubstituted benzene isomers; in the process described in U.S. Pat. No. 3,864,416 to separate alkyl-tetrasubstituted monocyclic aromatic isomers; in the process described in U.S. Pat. No. 3,668,267 to separate specific alkyl-substituted naphthalenes. Because of the commercial importance of para-xylene, perhaps the more well-known and extensively used hydrocarbon isomer separation processes are those for separating para-xylene from a mixture of C.sub.8 aromatics. In processes described in U.S. Pat. Nos. 3,558,730; 3,558,732; 3,626,020; 3,663,638; and 3,734,974 for example adsorbents comprising particular zeolites are used to separate para-xylene from feed mixtures comprising para-xylene and at least one other xylene isomer by selectively adsorbing para-xylene over the other xylene isomers.
In contrast, our invention relates to the separation of nonhydrocarbons and more specifically to the separation of fatty-acid esters. We have discovered that adsorbents comprising certain zeolites containing one or more selected cations at the exchangeable cationic sites exhibit adsorptive selectivity for an ester of an unsaturated fatty acid with respect to an ester of a saturated fatty acid thereby making separation of such esters by solid-bed selective adsorption possible. In a specific embodiment our process is a process for separating the unsaturated-fatty-acid esters methyl oleate and methyl linoleate from a mixture comprising methyl oleate, methyl linoleate and the saturated-fatty-acid esters methyl palmitate and methyl stearate.
Production of fatty esters is the most important phase in the industrial chemistry of fatty acids. The esters produced are of several types and include those resulting from the reaction of fatty acids with monohydric alcohols, polyhydric alcohols, ethylene or propylene oxide, and acetylene or vinyl acetate. The principal monohydric alcohols are methanol, 1-propanol, 2-propanol and 1-butanol. The greatest uses of esters are in the solvent and plasticizer fields. Esters of monohydric alcohols are used for plasticizers and in cosmetics. Esters of unsaturated fatty acids are used for drying agents.